The present invention relates to a method and apparatus for feeding reaction gases, advantageously oxygen and air or a mixture thereof, into a smelting furnace so that the cross-sectional area through which the gases are fed can be adjusted. Thus the velocity of the gases when they are discharged into the smelting furnace can be maintained sufficiently high with a varying quantity and quality of the gas.
When reaction agents and reaction gases are fed into a suspension smelting furnace, these are brought into contact with each other and mixed only in the reaction zone of the furnace. Now the mass transfer between the reacting solid particle and surrounding gas is rendered as high as possible in the reaction space itself, because the velocity difference between the reaction gas and the powdery solid matter also is made as great as possible.
From the U.S. Pat. No. 4,210,315 there is known an apparatus where the suspension of a powdery solid substance and a reaction gas is formed by feeding the solid substance into the reaction space centrally with respect to the reaction gas supply. Inside the solid substance feed pipe, there is coaxially installed a gas supply pipe wherethrough part of the gas is fed, and the bottom end the gas supply pipe is made conical so that gas is discharged through apertures provided at the bottom end of the cone. The gas emitted through the discharge apertures directs the solid substance falling along the conical surface towards the reaction gas zone proper, coming from outside the solid substance flow, i.e. towards the periphery of the reaction space.
From the U.S. Pat. No. 3,392,885 there is known a method and apparatus whereby the direction of the main reaction gas flow described in the above patent can be flexibly changed. By means of this apparatus, a horizontally supplied gas flow is divided to sub-flows radially with the aid of partition walls, and simultaneously the direction of the gas flow is turned to be parallel to the central axis of the reaction shaft of the smelting furnace, so that the velocity of the sub-flows increases at the same time. The sub-flows are discharged into the reaction space as an annular flow, thus encircling the concentrate flow supplied from the inside.
The U.S. Pat. No. 4,392,885 describes a method and apparatus whereby the major part of the reaction gas flow according to the U.S. Pat. No. 4,210,315 is fed symmetrically in several turbulent jets from around the pulverous substance flow into the reaction space. The discharge pipes, wherethrough the turbulent jets flow, are adjustable so that the degree and direction of turbulence therein can be adjusted.
The above described apparatuses designed for feeding pulverous substances, mainly concentrates, are perfectly usable as long as the amount of the material to be fed into the smelting furnace remains more or less the same. If the amount of concentrate to be fed into the smelting furnace is for some reason essentially reduced, the amount of supplied reaction gas must likewise be reduced. Generally there are no serious problems in feeding the concentrate; both measured and smaller amounts can normally be easily fed in through the same supply devices. However, a bigger problem arises with respect to the reaction gas to be supplied, for if the amount of gas is essentially reduced, its velocity in the discharge aperture also is reduced, because the transversal surface wherethrough it is fed still remains the same.
If the gas discharge velocity in the concentrate distributor and thus in the reaction zone of the furnace is essentially reduced, this causes difficulties in creating a good suspension in the reaction shaft, and as a consequence the reactions between concentrate and gas take place in an irregular and unsatisfactory manner. These difficulties are somewhat alleviated by means of the apparatus according to the U.S. Pat. No. 4,392,885, where the gas turbulence is intensified, but if the amount of gas falls for instance to half of the measured values, a good suspension is difficult to achieve even with this method. Another important reason for the diminishing of the reaction gas amount is that there is a growing tendency towards an intensified oxygen enriching, which naturally decreases the amount of employed gas.
According to the present invention, there is now developed a method and apparatus where the cross-sectional flow area, wherethrough the reaction gas flows, can be adjusted so that the flowing velocity of the reaction gases can be maintained sufficiently high, and thus a good suspension between the particles of the pulverous solid substance and the gas can be ensured in the reaction shaft of the furnace, in which case the desired reactions between the solid substance and the gas proceed rapidly.
Accordingly, the method of the invention for feeding reaction gases to the reaction shaft of a suspension smelting furnace is based on the fact that the gas distribution chamber is divided into several nested parts, so that gas can be fed in either through all annular sub-chambers, or only through one chamber, for example, depending on the amount of gas, and thus a sufficient gas velocity can be maintained all the time at the gas discharge aperture. Gas can be brought into the gas distribution chamber from one or several directions.
The pulverous material, such as concentrate, and fluxes may be fed centrally from inside the gas distribution chamber, by means of for instance the central jet distributor according to the U.S. Pat. No. 4,210,315 or the apparatus according to the U.S. Pat. No. 5,133,801. By means of the method of the invention, for example the air/oxygen ratio of the reaction gas can be adjusted steplessly, because the gas quantity is decreased while the oxygen ratio is increased, and this decreased amount of gas can now be fed in without using all sub-chambers.